Fix enforcement of restrictions inside regexp lookaround constraints.

tglsfdc · tglsfdc · commit f69c01f2c2b7 · 2015-11-07T12:43:24.000-05:00
Lookahead and lookbehind constraints aren't allowed to contain backrefs,
and parentheses within them are always considered non-capturing.  Or so
says the manual.  But the regexp parser forgot about these rules once
inside a parenthesized subexpression, so that constructs like (\w)(?=(\1))
were accepted (but then not correctly executed --- a case like this acted
like (\w)(?=\w), without any enforcement that the two \w's match the same
text).  And in (?=((foo))) the innermost parentheses would be counted as
capturing parentheses, though no text would ever be captured for them.

To fix, properly pass down the "type" argument to the recursive invocation
of parse().

Back-patch to all supported branches; it was agreed that silent
misexecution of such patterns is worse than throwing an error, even though
new errors in minor releases are generally not desirable.
diff --git a/src/backend/regex/regcomp.c b/src/backend/regex/regcomp.c
@@ -944,7 +944,7 @@ parseqatom(struct vars * v,
 			EMPTYARC(lp, s);
 			EMPTYARC(s2, rp);
 			NOERR();
-			atom = parse(v, ')', PLAIN, s, s2);
+			atom = parse(v, ')', type, s, s2);
 			assert(SEE(')') || ISERR());
 			NEXT();
 			NOERR();
diff --git a/src/test/regress/expected/regex.out b/src/test/regress/expected/regex.out
@@ -321,3 +321,8 @@ select 'a' ~ '()+\1';
  t
 (1 row)
 
+-- Error conditions
+select 'xyz' ~ 'x(\w)(?=\1)';  -- no backrefs in LACONs
+ERROR:  invalid regular expression: invalid backreference number
+select 'xyz' ~ 'x(\w)(?=(\1))';
+ERROR:  invalid regular expression: invalid backreference number
diff --git a/src/test/regress/sql/regex.sql b/src/test/regress/sql/regex.sql
@@ -82,3 +82,7 @@ select 'a' ~ '$()|^\1';
 select 'a' ~ '.. ()|\1';
 select 'a' ~ '()*\1';
 select 'a' ~ '()+\1';
+
+-- Error conditions
+select 'xyz' ~ 'x(\w)(?=\1)';  -- no backrefs in LACONs
+select 'xyz' ~ 'x(\w)(?=(\1))';

Original file line number	Diff line number	Diff line change
`@@ -321,3 +321,8 @@ select 'a' ~ '()+\1';`
`321`	`321`	`t`
`322`	`322`	`(1 row)`
`323`	`323`
	`324`	`+-- Error conditions`
	`325`	`+select 'xyz' ~ 'x(\w)(?=\1)'; -- no backrefs in LACONs`
	`326`	`+ERROR: invalid regular expression: invalid backreference number`
	`327`	`+select 'xyz' ~ 'x(\w)(?=(\1))';`
	`328`	`+ERROR: invalid regular expression: invalid backreference number`